Once conservation has finished evaluating and stabilizing the drawings they are sent to the large format queue in Digital Library Center. The DLC set up to digitize anything from film slides to three dimensional objects. For the Carrère and Hastings materials we employ the use of a large format scanner to get a large, detailed image.
The large format scanner is used when flat work is too big for the Copibooks. It works in the same way a large format film camera works; the larger the surface area of the negative the more detailed the photograph will be. Think of it as a super megapixaled digital camera. The difference between this camera and your average digital camera is this camera employs a progressive scan like your normal desktop scanner. It scans one line at a time, 8000 lines for each image (http://betterlight.com/superModels.html). Because it is a progressive scan type of camera, the document cannot move otherwise streaks will appear in the image. To solve this problem the document is held down with a vacuum table. This also helps eliminate any wrinkles of folds that the document might have. Of course these documents have had, and have, a life of their own and are subject to folds and creases that need to be minimized while caring for the document. To remedy this, we use lighting and reflectors to eliminate wrinkles much like fashion photographers do. One problem we have run into is scanning drawings on tracing paper. The vacuum table is black as to absorb light and not put glare onto what we are scanning, but for many of these drawings the black shows through the tracing paper effectively eliminating the drawing from the scanned image. Our solution has been to first lay down some porous white vellum then place the document on top. We lose some of the vacuum’s power but the resulting image has been much more satisfactory.